1. Field of the Invention
The field of the invention is that of vehicle instrument panel or cockpit display systems. The invention especially applies to the field of civil or military aircraft. It can also apply to road, sea or rail transport means.
2. Description of the Prior Art
At present, the instrument panels of the cockpits of modern aircraft comprise display screens and instruments over the majority or their area, thus reducing the direct vision of the external scene in the bottom zone of the cockpit. In a certain number of applications, including visual flight at low altitude, this absence of direct vision can be annoying.
A simple first solution consists in the pilot contorting himself in order to see above display screens, when this is possible.
A second solution consists in using collimated display systems, also called “See Through” systems. These essentially comprise two large families which are the helmet-mounted displays worn on the pilot's head and so-called “Head-Up Display” devices permanently fitted in the cockpit. These devices superimpose information in the form of images or symbols on the external scene.
These latter equipments have the feature of being collimated, that is to say that the items of information coming from a display device are projected “to infinity” by means of suitable optics. The pilot does not therefore need to focus on either the information or the scene, both being clearly seen simultaneously. These equipments have a certain technical complexity and are therefore of high cost. Moreover, the information is presented specifically so as not to mask the scene in the background, which involves a representation different from that of the so-called “Head-down” screens. The pilot must therefore put a certain amount of effort into going between his “head-up” and “head-down” screens in order to find his landmarks.
A third solution consists in using semi-transparent display screens placed in the user's field of vision and which make it possible to project an image superimposed on the external scene. The advantage of these screens is that it is possible to obtain large display areas visible in a large field of vision at costs that are lower than those of collimated systems. The principal disadvantage of these screens is that the image is not collimated, which can give rise to problems of parallax and accommodation.